Experiment Study For Flexural Behavior Of Concrete Beams Reinforced With Hybrid FRP And Steel Bars

At present,there are many factors that cause the durability of concrete structure to be reduced,including concrete carbonization,the corrosion of rebar,freezing and thawing,physical and chemical action in the environment of erosion,and the corrosion of rebar is the most prominent.Fiber reinforced composites?referred to as FRP?as a new composite material,which has the advantages of high strength,corrosion resistance and light quality,has great development potential in concrete structure.The structural performance degradation caused by rebar rust can be effectively solved by the reasonable arrangement of FRP bars or the substitution of corner bars which are prone to rust,and the durability of concrete structures can also be improved.This paper is based on the National Natural Science Foundation“Design and performance of reinforced concrete members with FRP tendons and common reinforcement with durability?51578267?”,the flexural properties of the concrete beams reinforced with hybrid FRP bars and steel bars are studied by theoretical analysis and experimental research,the main work is as follows:1.Experimental study on mechanical properties and bonding properties of FRP bars.Selecting basalt fiber reinforced composites?BFRP?bar,carbon fiber reinforced composites?CFRP?bar and glass fiber reinforced composites?GFRP?bar,through the tensile test of FRP bars and the bond test of FRP reinforced concrete specimens,the failure modes of tensile test and bonding test of FRP bars and the difference between FRP bars and rebar properties are compared,and the tensile strength,elastic modulus and bond strength of FRP tendons are obtained.The results show that the ultimate tensile strength of FRP bars is greater than that of steel bars,about 1.37³.29 times of steel bars,but the elastic modulus is about20%⁶7%of steel bars.The bonding strength can be increased by surface sand blasting or processing rib to increase the mechanical bite force between FRP bars and the concrete,so it is feasible to use FRP bars to participate the hybrid reinforcement in the concrete structures.2.Study on the design theory of concrete beam reinforced with hybrid FRP bars and steel bars?hereinafter referred to as"hybrid reinforced"?.According to the principle of"equal strong replacement",two kinds of hybrid reinforcement ratios are defined according to the conversion of strength and elastic modulus.Combined with the design code of concrete structure and foreign related specifications,this paper analyzes the stress stage and failure mode of hybrid reinforced concrete beam.Deduceing the calculation formula of crack moment and ultimate moment based on the assumption of plane section and obtaining the calculating theoretical formulae of average crack spacing,crack width and deflection through taking into account the difference of bond properties between FRP bars and steel bars.The related content can provide a reference for the design of hybrid reinforced concrete beam and the formulation of relevant specifications.3.Experimental study on flexural behavior of concrete beams reinforced with hybrid FRP bars and steel bars.Selecting suitable GFRP bars and BFRP bars,8 concrete beams reinforced with FRP bars and steel bars and 3 ordinary reinforced concrete beams have been designed and tested,the crack moment,the ultimate moment,the load-deflection relation,the crack initiation process,crack width and spacing of the hybrid reinforcement concrete beams are compared and analyzed with the reinforced concrete beams.The test results show that,it is feasible to use FRP bars to replace corner bars under equal strong replacement conditions,the bearing capacity of the hybrid reinforced concrete beam is reduced by about 3%⁹%.Under the same load level,the deflection of the hybrid reinforced concrete beam is about1.2¹.94 times of the reinforced concrete beam,and the maximum crack span is about 1².63times.According to the relative test results of domestic and foreign scholars,the correctness of calculation formulas of bearing capacity,crack and deflection of mixed reinforced concrete beams is verified by the comparison between the experimental values and the theoretical calculation values.The relevant test and theoretical analysis results can provide some reference for practical engineering application of mixed reinforced concrete members.4.Analysis of the ductility properties of the concrete beam reinforced with hybrid FRP bar steel bar.Based on the flexural behavior test of the hybrid reinforced concrete beam,the calculation method of ductility index is discussed from the traditional ductility coefficient,energy ductility coefficient and deformation coefficient,and the ductility variation law of the hybrid reinforced concrete beams is analyzed with the experimental ststistics.The results show that the ductility of hybrid reinforced concrete beams decreases with the increase of the hybrid reinforcement ratio and the ratio of FRP bars to steel bar area.In order to ensure the good ductility of the hybrid reinforced concrete beams with GFRP bar,it is suggested that the hybrid reinforcement ratio?_h,s is 0.8%¹.26%and the area ratio of FRP bar to steel bar in tensile region is not more than 1.28.